Also - I hadn't updated mine for a while so I think I still had v3.30 The first time I ran the update it said it was updating verion 3.30. After the failure, on the second install it said it was updating v3.10

I should remember this by now, but how do you find the current software version on the unit? (60Cx).

There are a couple of options.
On recent firmware, Go to the Main Menu, then select or press Tracks:Enter:Setup:Enterata Card Setup:Enter:Menu:Card Info:Enter
On any firmware, but you can start Mapsource and read maps from the GPS. In the tab for 'maps' it will display a total of the space used.
Alternately, you can put the GPS into Mass Storage mode and view the disk usage on it from your favorite computer.

3.

Why do I sometimes see two firmware version numbers displayed?

If you see two version numbers displayed, the first is the main OS of the receiver. The second is the version of the code used by the Sirf receiver circuit.